The invention relates to a cable terminator, preferably an outdoor terminator for high voltage according to the preamble of the main claim.
Various types of terminators are known. Older designs are formed with porcelain insulators and an oil or other chemical filling. Such terminators have the disadvantage that they are not very robust mechanically, and no longer fulfil present-day environmental protection conditions with regard to possible substance leakage. A terminator without oil filling is described in EP 667 665 B1. A special feature of this is a rigid conducting element which is designed to take up lateral forces. The forces are carried away from the overhead conductor connection via the rigid conducting element, via a base body with a field control and insulating device, to the bearing structure. No field-controlling coating is present on the surface of the terminatorxe2x80x94in particular in the region of the rigid conducting element.
An object of the invention is to propose a cable terminator, preferably a high-voltage outdoor terminator, which can be produced at low cost, is mechanically stable and is controlled in an electrically reliable manner.
The object is achieved by the features of the main claim. Further embodiments are found in the subclaims.
The terminator is mounted at one end on a base fitting, preferably for fastening to a cross-arm. Means for fastening the cable are formed on the base fitting and have an electrical duct inside the terminator. Situated at a top fitting are means for fastening an electrical conductor to the duct; means for electrically connecting the cable shield to earth potential and means for the field control and insulation at the inhomogeneous potential transitions at the cable end are present.
The insulating body generally bears on its surface an elastomeric material (preferably of silicone rubber) with a ribbed surface (shielding plates). The length and in particular diameter of the insulating body is to be chosen such that the demands for sufficient insulation and avoidance of atmospheric flashovers at full operating voltage are met. This requirement can be fulfilled by covering the surface of the insulating body with a voltage-dependent control coating. The diameter of the insulating body can then also be kept particularly small. The control coating is formed on the basis of microvaristors, preferably ZnO microvaristors (WO 9726693 A1). The preferred embodiment comprises ZnO ceramic particles which are embedded in a polymer matrix in a proportion of 60 to 75 per cent by weight. The ZnO particles are doped with mixed oxides in the order of 10% based on oxides of Bi, Cr, Sb, Co, Mn and further possible elements in smaller proportions. The polymer composition may be silicone rubber or polyethylene, depending on the base material of the carrier body. In the present case, the layer forming the control coating is formed inside the insulating-body casing designed with shielding plates. This layer according to the invention has the effect of changing the potential profile in such a way that the field lines are pushed more to the upper end of the terminator, so that, as a result of the changed electrical field distribution, voltage spikes or overvoltages at the location of the cable conductor connection are avoided. The effect of the field-strength-dependent control layer is described in detail in the article in Elektrizitxc3xa4tswirtschaft, 99 (2000), pages 68-73.
The insulating body is fastened to the base fitting. This type of fastening corresponds to the prior art (EP 667 665 B1). The customary means for electrically connecting the cable shield to earth potential and means for the field control (field control bodies) and insulation at the inhomogeneous potential transitions at the cable end are employed. What is essential is that, on the fastening to the base fitting, voids present between the cable end and the field control and insulating elements are closed by mechanical bracing with the base fitting.
The electrical duct, designed as a tube or as a pin, is connected to the cable conductor via contact elements and the electrical duct, the insulating body and the top fitting form a unit for assembly. The parts consisting of electrical duct with contact elements, insulating body and top fitting are produced separately. The top fitting consists essentially of a conductive end plate and a conductor connection piece, in which a thread may be incorporated for the fastening of a carrying lug. The electrical duct is preferably fastened inside the end plate by welding (or by another firm mechanical connection). The insulating body, consisting of insulating material, is bonded into the top fitting. The unit thus produced is lifted by a crane at a carrying lug into the assembly position and lowered from above over the prepared lower part of the terminator. The dimensions of the parts in the lower region of the arrangement forming a unit are designed such that upon assembly they slide in a self-centring manner into the base structure on the base fitting.
A contact is preferably fastened to the cable conductor with screws. The contact, in the form of a plug connection to the electrical duct, is provided by contact laminations. This plug connection is not designed to take up the forces on the terminator. In the present arrangement, the insulating body is therefore constructed and dimensioned so as to be able to take up all the mechanical forces. The plug connection is then free from mechanical loads. A typical magnitude of the transverse force to be expected is 5 kN, so that the mechanical design is to be dimensioned for this characteristic quantity.
The insulating body is produced from cast resin or another suitable material. It may be materially strengthened, for example with glass fibres. The insulating body is completely filled up with material from the bottom edge up to the level of the contact elements. A cavity is preferably formed in the interior of the insulating body. The cross-section of the cavity (the space filling) may be linear or be reduced in a curve in the shape of a funnel towards the top fitting. The form of the cavity allows the weight to be kept low, but the wall thickness may not be reduced further than a point where the bending forces can be taken up. In a preferred design, the inner surface of the cavity is lined with a conductive coating.
The essential process steps during assembly are as follows:
preparation of the cable end, stripping the end insulation and uncovering the cable conductor
attachment of the contact receptacle to the cable conductor
fastening of the base structure to the base fitting
by means of a crane, lifting of the assembly unit consisting of insulating body, top fitting and electrical duct
lowering of the assembly unit onto the base structure fastened to the base fitting
the parts are located in a self-centring manner
fastening and bracing of the assembly unit to the base fitting
fastening of the overhead conductor to the top fitting via a current terminal.